1. Field of the Invention
The present invention relates to a light receiving element module and a manufacturing method therefor and, more particularly, to a light receiving element module in which light receiving elements are connected to one another using an inter-element connecting body that connects, in series, the light receiving elements including both of positive electrodes and negative electrodes on one principal plane side.
2. Description of the Related Art
A light receiving element module has been disclosed in which a plurality of light receiving elements, on a light receiving surface side of which electrodes are not provided and on a non-light receiving surface side of which positive electrodes and negative electrodes are provided, are provided side by side lengthwise and breadthwise, and a positive electrode of one light receiving element and a negative electrode of a light receiving element adjacent to the light-receiving element are connected by an inter-element connecting body called inter connector.
In such a light receiving element module, in general, to electrically connect a positive electrode formed on the rear surface of a first light receiving element and a negative electrode formed on the rear surface of a second light receiving element, the elements are connected by the inter-element connecting body. As the inter-element connecting body, in general, metal having high conductivity such as a copper foil entirely covered with solder is used. In the connection of the inter-element connecting body, the inter-element connecting body is arranged on a positive electrode or a negative electrode, which are element electrodes (hereinafter also referred to as electrodes) made of metal such as silver, and heated to compression-bond the inter-element connecting body and the element electrodes partially or over the entire length.
In the case of a light receiving element of a back connection type, only on one surface of which both positive and negative electrodes are arranged, the inter-element connecting body only has to be mounted on the back of the light receiving element. Therefore, the inter-element connecting body does not cover a light receiving surface of the light receiving element. Therefore, it is possible to increase the thickness of the shape of the inter-element connecting body and the element electrodes. It is possible to reduce resistance for collecting electricity in the element and resistance for connecting elements. There is an advantage that the light receiving element is excellent in efficiency of converting light into electricity, that is, photoelectric conversion efficiency.
As such a light receiving element module of the back connection type, there is a light receiving element module in which a large number of elongated linear electrodes are collectively connected to a bus electrode or a current extraction electrode at ends of elements and connected to the current extraction electrode using an inter-element connecting body (Japanese Translation of International Application No. 2010-521811). In such a light receiving element module, a generated current is collected to the end of the element by the large number of elongated linear electrodes. An electric current flows from the end to the element adjacent to the element through the inter-element connecting body.
A solar battery element is also proposed in which positive and negative electrodes are formed in a two-layer structure via an insulating layer on an element (Japanese Patent Application Laid-Open No. 2001-189475). In this structure, it is possible to increase an electrode area per projection area of the element compared with Japanese Translation of International Application No. 2010-521811. As a result, current collection resistance with respect to a light reception current is reduced, and thus it is made possible to reduce a power loss due to resistance.
Another light receiving element module is also disclosed in which a resin sheet provided with a metal electrode having a pattern equivalent to the pattern of a positive electrode and a negative electrode on an element rear surface is arranged with respect to an element, on the element rear surface of which the positive electrode and the negative electrode are formed, and element electrodes among a plurality of the elements are connected using the metal electrode on the resin sheet as an inter-element connecting body and a current extraction electrode (Japanese Patent Application Laid-Open No. 2010-245399).
Another solar battery module is also disclosed in which positive and negative element electrodes are formed in a two-layer structure on the rear surface of a cell (a light receiving element) and a connection line is arranged over the entire element to overlap the element electrodes to reduce current collection resistance with respect to a photocurrent and reduce a power loss due to resistance (Japanese Patent Application Laid-Open No. 2009-206366).
In the element structure of Japanese Translation of International Application No. 2010-521811, the large number of elongated linear electrodes collect the generated current to the end of the element. The linear electrodes are collectively connected to the bus electrode or the current extraction electrode at the end of the element. The inter-element connecting body is connected to the current extraction electrode. An electric current flows to the adjacent element through the inter-element connecting body. However, in such a structure of the element, the generated current needs to be collected to the end of the element by the linear electrode, and a resistance loss during the current collection is relatively large. In Japanese Translation of International Application No. 2010-521811, a positional relation between the positive electrode and the negative electrode of the element electrode on a plane is fixed. Therefore, it is necessary to form strings formed by plurality of elements and arrange and connect a conductor between the strings in a portion where the strings are connected, that is, a turning-back portion of the strings. Therefore, an area is necessary in a portion other than the elements. The photoelectric conversion efficiency of a module cannot be improved.
In Japanese Patent Application Laid-Open No. 2001-189475, the positive and negative electrodes of an element are dividedly formed in two layers. It is costly to form the element having such a structure. Although one electrode covers the entire element rear surface, it is difficult to increase the thickness of the electrodes on the element and attain a sufficient reduction of current collection resistance. A power loss due to resistance cannot be sufficiently reduced.
In Japanese Patent Application Laid-Open No. 2010-245399, a resin film on which the metal pattern is formed is used as an inter-element connecting body without forming a current extraction electrode and a bus electrode on the element. In modularization, it is necessary to align the inter-element connecting body and the electrodes on the light receiving element. Therefore, in the module structure of Japanese Patent Application Laid-Open No. 2010-245399, an interval necessary for preventing a short-circuit between the positive electrode and the negative electrode depends not only on a positional accuracy of the element electrode but also alignment accuracy between the element and the resin film. For example, when an alignment mark is put in the element for highly accurate alignment, it is necessary to introduce a step of forming the alignment mark. When the alignment mark is formed by a silver electrode, silver is necessary for the formation of the alignment mark. Apparatus costs increase because of a highly accurate aligning mechanism. Besides, photoelectric conversion efficiency is deteriorated in an alignment mark section.
In Japanese Patent Application Laid-Open No. 2009-206366, the positive and negative electrodes are formed on the light receiving element rear surface in the two-layer structure. The inter-element connection line is arranged over the entire electrode to overlap the element electrode. Therefore, although the current collection resistance with respect to the photocurrent is reduced, the reduction is insufficient. There is a demand for a reduction in a power loss through a further reduction in resistance.
However, according to the related art, the alignment accuracy between the element electrode and the inter-element connecting body is insufficient. A reduction in the power loss due to the current collection resistance is insufficient. There is a demand for further improvement of the photoelectric conversion efficiency.